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  Always begin with visual acuity, the vital sign of the eye.

  
  
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  The patient should be instructed to remove contact lens and not to put them back in until the symptoms have resolved.

  
  
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  The presence of pain and the relief of pain with instillation of anesthetic agents are helpful in determining the cause of red eye.

  
  
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  Follow a systematic approach to the physical examination: visual acuity, lids and lashes, conjunctiva, sclera, cornea, pupil examination, and anterior chamber.

  
  
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  Never prescribe topical steroids without consulting with an ophthalmologist.

Eye complaints account for 3% of all emergency department (ED) visits. Red eye is a common complaint, and although most cases are benign, self-limited conditions, some may be vision-threatening. Conjunctivitis is the most common cause of a red eye, but other frequent problems include subconjunctival hemorrhage, corneal injuries (abrasions, keratitis, and foreign bodies), and acute uveitis.

Conjunctivitis may be viral, bacterial, or allergic. Viruses are the most frequent cause, especially adenovirus. The most common bacterial pathogens are Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae. Chlamydia trachomatis or Neisseria gonorrhea are unusual, but important causes of conjunctivitis. Allergic conjunctivitis is due to recurrent seasonal inflammation from allergen exposure. About 15% of the population will experience allergic conjunctivitis at one time in their life.

Subconjunctival hemorrhage is blood between the conjunctiva and sclera that results from a ruptured conjunctival blood vessel. Subconjunctival hemorrhage is caused by direct trauma or indirect injury. Although it may be alarming to the patient, it is usually a benign process that occurs with a sudden increase in pressure from sneezing, coughing, straining, or vomiting. If atraumatic, the etiology is usually hypertension or spontaneous rupture.

Corneal injury is common because the epithelium is thin and easily damaged. Corneal abrasions are particularly common, representing 10% of all ED visits for eye complaints. The cornea is resistant to infection, but when injured, a potential portal to bacteria is created. Viral infections that cause injury to the cornea include herpes simplex and varicella (ie, herpes zoster ophthalmicus). Contact lens use may predispose the patient to keratitis or a corneal ulcer due to gram-negative bacteria.

Acute anterior uveitis is defined as inflammation of the iris and ciliary body. The most common cause is trauma, with patients usually presenting 1–4 days after the precipitating event. Systemic causes include ankylosing spondylitis, Reiter syndrome, inflammatory bowel disease, and chronic granulomatous conditions like tuberculosis or sarcoidosis. Infectious ulcerations can also cause anterior uveitis.

History

The single most important historical feature that helps determine the cause of red eye is the presence of eye pain. Conjunctivitis is characterized by a gritty foreign body sensation and tearing or discharge, but it is usually not particularly painful. Viral (ie, adenovirus) and allergic sources tend to be pruritic with watery discharge, but suspect bacterial infection with mucopurulent discharge. An infectious source often begins unilaterally and spreads through autoinoculation. Constitutional symptoms such as fever, rhinorrhea, and myalgias suggest a systemic viral illness. Allergic conjunctivitis is associated with more intense itching and seasonal history.

Similarly, subconjunctival hemorrhage is a painless condition. Patients usually present to the ED merely because the appearance of blood on the sclera of the eye is concerning to the patient.

Eye pain is produced when the epithelium of the cornea is injured or there is inflammation to deeper structures (ie, iris). Corneal abrasions due to trauma or foreign body are characterized by pain, foreign body sensation, tearing, and photophobia. A history of working with power tools and metal should raise the suspicion of a foreign body. If the abrasion is large enough, patients may complain of decreased vision. Contact lens use or exposure to ultraviolet light should be ascertained and raises the suspicion for corneal inflammation/infection (ie, keratitis).

Acute anterior uveitis presents with a gradual onset of a painful red eye with severe photophobia and diminished vision. The patient will prefer to sit in a dark room with a hand over the eye.